Membrane switch and production method thereof

ABSTRACT

A membrane switch comprising a pair of electrode plates and a spacer separating the plates, wherein the operating force required to operate the membrane switch by pressing it with a rod having a hemispherical tip with a radius of curvature of 5 mm is within the range of 0.03 to 0.2 kg. The spacer is in the form of a film, the film has through holes, and the aperture ratio of the through holes is 50% or above. The effect is that a membrane switch exhibiting no malfunction, negligible variation in the operating force, and excellent in durability can be obtained.

TECHNICAL FIELD

The present invention relates to an improvement of a switch for anon-vehicle horn.

More particularly, it is directed to the provision of a membrane switchfor an on-vehicle horn that does not malfunction, exhibits negligiblevariation operating force, and is excellent in durability.

BACKGROUND ART

Conventionally, a switch for an on-vehicle horn, especially a membraneswitch, basically comprises, as shown in FIG. 4, a pair of electrodeplates 12 having an insulating film 13 placed thereon (for example, apolyester film with a conducting metal such as aluminum evaporatedthereon, or copper foil) and a spacer (for example, a polyester film) 11interposed between the electrode plates at a predetermined distance 14,in which connection terminals 15 for lead wires or the like are attachedto the electrode plates 12 and electrically connected to the vehiclebody side.

Known examples of such membrane switches include: (i) a type in whichthe spacer is made of foam plastics (U.S. Pat. No. 4,882,460); (ii) atype in which the spacer is provided in the interior surface of theouter cover (U.S. Pat. No. 5,265,904); and (iii) a type in which thespacer is constituted of projections (dots) 16 formed on an electrodeplate 12 by printing with a thermosetting resin ink as shown in FIG. 5.

FIG. 4 is a sectional view showing a typical structure of a membraneswitch.

FIG. 5 is a schematic diagram showing the structure of a spacercomprising a conventional membrane switch.

Referring to FIGS. 4 and 5, reference numeral 11 denotes a spacer, 12denotes an electrode plate, 13 denotes an insulating film (base plate),14 denotes a gap, 15 denotes a connection terminal, and 16 denotes aprinted-dot spacer.

(i) When the spacer is made of foam material, there is such a dangerthat its height of the spacer is gradually reduced by repeated loadapplied thereon and its operating force is thereby changed and thereforeresults in the drawback of deficient durability.

(ii) When the spacer is provided on the surface of the outer cover, itsoperating force varies with the position of the push given thereonbecause the distances between the projections, serving as the spacer,are large.

(iii) When the spacer is provided with printed projections:

(A) variations in the operating force are caused by variations in theheight of the dotted objects;

(B) a malfunction tends to occur such that the switch becomes contacted,while it is expected to be separated, because the printed dots cannot bemade sufficiently high; and

(C) the fabrication process becomes complicated because, in addition tothe formation of the printed dots, provision of an adhesive layer on thecircumference of the electrode is required to laminate two electrodes.

DISCLOSURE OF THE INVENTION

The inventors, after various investigations of the above mentionedproblems, found that a membrane switch which has no malfunction, smallvariation in the operating force, and is excellent in durability can beprovided by giving, in a membrane switch, a specific thickness to thespacer and a specific size to the through hole in the spacer to therebykeep the operating force within a predetermined range and, thus,completed the present invention.

Namely, the invention:

(1) provides a membrane switch comprising a pair of conductive electrodeplates confronting each other and a spacer separating the same, whereinthe operating force required to operate the switch by pressing it with around rod having a hemispherical tip with a radius of curvature of 5 mmis within the range of 0.03 to 0.2 kg; and

(2) it is also characterized in that the spacer is in the form of afilm, the film has through holes, and the aperture ratio of the throughholes is 50% or above. It further

(3) provides a method of fabricating the membrane switch mentioned in(1) or (2) in which the operating force is kept within the range of 0.03to 0.2 kg by setting the thickness of the spacer and the size of thethrough hole in the spacer to predetermined values;

(4) it is also characterized in that the thickness of the spacer is20-150 μm and the size of one through hole in the spacer is 2-10 mmsquare; and

(5) it is also characterized in that an insulating film with apredetermined thickness and having predetermined through holes madetherein is used as the spacer.

Referring to the drawings, the invention is described below in concreteterms.

The present invention basically is a membrane switch comprising a pairof conducting electrode plates disposed confronting each other and aspacer inserted therebetween, wherein the operating force required tooperate the membrane switch by pressing it with a round rod with ahemispherical tip having a radius of curvature of 5 mm is within therange of 0.03 to 0.2 kg, or preferably within the range of 0.05 to 0.15kg.

As the spacer, it is preferable to use an insulating film with specificthrough holes made therein.

In this case, when the operating force is less than 0.03 kg, amalfunction tends to occur such that the conducting electrode plates arestill electrically in contact to each other even if the switch isreleased to be off. When it exceeds 0.2 kg, a malfunction tends to occursuch that the line is not conducting even if the switch is pressed to beon. Either case is not desirable.

While the portion other than the through holes of the insulating filmserves as the spacer, it is preferred that the pair of confrontingconducting electrode plates are insulated from each other by the spacerwhen the membrane switch is not pressed and they become definitelyconducting when the membrane switch is pressed to blow the horn.However, the spacer, especially the shape of the through hole, is notlimited to the shape shown in the figure, but that in a circular,elliptical, polygonal, and other shape can be suitably used.

In the invention, by setting the thickness of the spacer and the size ofthe through hole to predetermined values, a membrane switch having anoperating force of 0.03-0.2 kg, without no malfunction and excellent indurability can be provided.

Accordingly, to keep the operating force within 0.03-0.2 kg, it ispreferred that the thickness of the spacer be set to 20-150 μm, or morepreferably to 25-125 μm, and the size of the through hole, when it isfor example of a square shape, be set to 2-10 mm square, or morepreferably to 2.5-8 mm square.

The operating force can be decreased according to enlarging the apertureratio of the through hole in the spacer.

However, insofar that the spacer must maintain insulation betweenelectrode plates, portions other than the through holes must be left.Therefore, an aperture ratio of 50% to 80% is preferable. The pitchdistance of the through holes is normally 0.5-2.0 mm, or preferably1.0-1.5 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1-(A) is a sectional view of a membrane switch of Example 1 andFIG. 1-(B) is a schematic diagram showing the structure of the spacer inExample 1.

FIG. 2 is a sectional view of the membrane switch of Example 6.

FIG. 3-(A) is a schematic diagram showing structure of the spacer ofExample 7. FIG. 3-(B) is a sectional view of the membrane switch ofExample 7.

Referring to FIGS. 1—3 reference numeral 1 denotes a spacer, 2 denotescopper foil, 3 denotes a base film, 4 denotes an adhesive, 5 denotes athrough hole, 6 denotes a hot melt adhesive, 7 denotes an insulatingfilm, and 8 denotes a margin to paste up.

FIG. 4 is a sectional view showing a typical structure of the membraneswitch.

FIG. 5 is a schematic diagram explanatory of the structure of the spacerconstructing a conventional membrane switch.

Referring to FIGS. 4 and 5, reference numeral 11 denotes a spacer, 12denotes an electrode plate, 13 denotes an insulating film (base plate),14 denotes a gap, 15 denotes a connection terminal, and 16 denotes aprinted dot spacer.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in detail as related to the followingexamples, which, however, do not limit the scope of the presentinvention.

EXAMPLE 1

As shown in FIG. 1, a copper foil of 35 μm thickness (100 mm×50 mm) 2was laminated onto a base material (100 mm×50 mm) 3 made of a 125μm-thickness PET (LUMILAR manufactured by Toray Industries, Inc.) whichwas coated with a 50 μm-thick layer of a polyolefin-based hot-meltadhesive 6 by bonding them together by thermo-compression to produce abase plate. A sheet (90 mm×40 mm) of a 50 μm thickness PET film (TorayInc. made “Lumirror”) with grating-shaped through holes (5 mm×5 mm) 5made therein at a pitch width of 6 mm, used as the spacer 1, wassandwiched between two sheets of the base plates, with the copper foilside turned inward, and further, with an adhesive film (NITTO DENKO Inc.made “No. 5911”) 4 placed on the circumference of the spacer 1, theywere bonded by thermocompression and, thus, a membrane switch wasfabricated.

A push rod having a hemispherical tip with a radius of curvature of 5 mmwas placed on the surface of the membrane switch and a load was appliedto the push rod and, thereby, the load to operate the switch wasmeasured as the operating force.

To test the durability of the switch, it was pressed with a constantforce (normally, 100 g/cm2) 10,000 times and, thereafter, the oneexhibiting no malfunction and a small change in the operating force(within 20% or so) was taken as a good one.

The results are shown in Table 1.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Spacer PET Film PET Film PET Film PET Film PET Film PET FilmPET Film Material Spacer 50 μm 50 μm 50 μm 25 μm 125 μm 50 μm 50 μmThickness Aperture 69% 51% 79% 69% 69% 69% 69% Ratio Operating 0.1 kg0.13 kg 0.05 kg 0.05 kg 0.15 kg 0.1 kg 0.1 kg Force Durability Good GoodGood Good Good Good Good

EXAMPLE 2

The same processes as in Example 1 were performed except that the sizeof the through hole in Example 1 was set to 2.5 mm×2.5 mm. The resultsare shown in Table 1.

EXAMPLE 3

The same processes as in Example 1 were performed except that the sizeof the through hole in Example 1 was set to 8 mm×8 mm. The results areshown in Table 1.

EXAMPLE 4

The same processes as in Example 1 were performed except that thethickness of the PET film in Example 1 was set to 25 μm. The results areshown in Table 1.

EXAMPLE 5

The same processes as in Example 1 were performed except that thethickness of the PET film in Example 1 was set to 125 μm. The resultsare shown in Table 1.

EXAMPLE 6

As shown in FIG. 2, a base plate was produced by thermocompressionbonding a 35 μm thickness copper foil (90 mm×40 mm) 2 onto a PET filmbase material (100 mm×50 mm) 3 coated with the adhesive as in Example 1.

The same spacer 1 as in Example 1 was placed on the copper foil and thetwo electrode plates 2 were thermocompression bonded therewith. Theresults are shown in Table 1.

EXAMPLE 7

As shown in FIG. 3, a 50 μm-thick PET film (100 mm×50 mm) having throughholes of 5 mm×5 mm formed at a pitch of 6 mm in the center area (90mm×40 mm) with the margin 8 left for applying paste, was sandwiched, asa spacer 1, between the same base plates as in Example 6 and they werebonded together thermocompression. The results are shown in Table 1.

COMPARATIVE EXAMPLE 1

Dot-like projections were printed with urethane-acrylate base UV-cureink on the copper foil of the base plate in Example 1, and then, anadhesive layer was provided on the circumference of the copper foil andthe base plate was laminated with the other unprinted base plate bythermo compression bonding.

The drawback of the resulting product was that the inter-electrodedistance was insufficient and the switch did not get off immediatelywhen a press on the membrane switch was released.

COMPARATIVE EXAMPLE 2

The same processes as in Example 1 were performed except that thethickness of the PET film in Example 1 was set to 12 μm and the size ofthe through hole was set to 2.5 mm×2.5 mm.

The drawback of resulting product was that the inter-electrode distancewas insufficient and the switch did not extinguish immediately when apress on the membrane switch was released.

COMPARATIVE EXAMPLE 3

The same processes as in Example 1 were performed except that thethickness of the PET film in Example 1 was set to 188 μm and the size ofthe through hole was set to 8 mm×8 mm.

As a result, the operating force became as high as 0.35 kg and wasaccompanied by a problem of a malfunction of the membrane switch notconducting even if it was pressed to be on.

EXAMPLE 4

The same processes as in Example 1 were performed except that the sizeof the through hole in the PET film in Example 1 was set to 1.7 mm×1.7mm.

As a result, the operating force became as high as 0.23 kg and wasaccompanied by a problem of a malfunction of the membrane switch notconducting even if it was pressed to be on.

EXAMPLE 5

The same processes as in Example 1 were performed except that the spacerin Example 1 was replaced with a polyurethane foam film of a thicknessof 200 μm.

The obtained result was accompanied by a problem of considerablevariation of its operating force while the operation to press the switchwas repeated, i.e., it was deficient in durability.

According to the present invention, as described in the foregoing, amembrane switch exhibiting no malfunction, negligible variation in theoperating force, and excellent in durability can be obtained.

What is claimed is:
 1. A membrane switch comprising a pair of conductiveelectrode plates confronting each other and a spacer separating theelectrode plates, wherein an operating force required to operate themembrane switch by pressing the conductive electrode plates togethercorresponds to a force exerted by a round rod having a hemispherical tipwith a radius of curvature of 5 mm at a range of 0.03 to 0.2 kg; andwherein the spacer is in a form of a film having through holes ataperture to spacer ratio of 50% or more.
 2. The membrane switchaccording to claim 1, wherein the spacer has a thickness of 20 to 150 μmand has through holes each having a size of 2 to 10 mm square.